More than 1 million cases of nonmelanoma skin cancer and 59,600 cases of melanoma are diagnosed yearly in the United States, resulting in about 10,600 deaths (about 7,800 due to melanoma) in 2005. In recent years it has become clear that UV-damaged skin has an increased chance of developing one of the forms of skin cancer, including basal cell carcinoma, squamous cell carcinoma and cutaneous malignant melanoma. The apoptotic response to UV is a protective response that eliminates cells that receive high doses of UV. While most studies have focused on DNA damage-inducible, p53-dependent pathways of UVinduced apoptosis, membrane receptor mediated signaling pathways also play an important role in inducing apoptosis. UV-irradiation activates kinases that phosphorylate the alpha subunit of eukaryotic initiation factor 2 (elF2a ) and subsequently inhibit protein synthesis. Translation plays an important role in regulation of apoptotic gene expression. However, the upstream signaling pathway(s) that leads to elF2a kinase(s) activation upon UV-irradiation is not known. The objective of this application is to elucidate the mechanisms that regulate UV-induced apoptosis via nitric oxide synthase (NOS) mediated signaling pathways and to determine the roles of nitric oxide (NO)/peroxynitrite (ONOO~) and zinc (Zn2+) in UV-induced translation regulation and apoptosis. The research proposed in this application is significant because understanding the regulation of NOS activation and how this regulation affects elF2a kinase(s) activation and/or apoptosis upon UV-irradiation will lead to a new signaling network for identification of target genes and development of therapeutics in the prevention and treatment of UV-related cancers. In Specific Aim I, we propose to elucidate the UV-induced and NOmediated signaling pathway(s) that leads to elF2ct phosphorylation. The working hypothesis is that NO mediates UV-induced activation of elF2a kinase(s), which phosp_horylate elF2a . In Specific Aim II, we propose to determine the mechanism and kinetics of NO/ONOO" production and their role in UV-induced apoptosis. The working hypothesis is that at a high ratio of NO:ONOO~, the effect of UV can be antiapoptotic, while at a low ratio this effect can be pro-apoptotic. In Specific Aim III, we propose to determine the role(s) of Zn in UV-induced ER-stress and apoptotic signaling pathways. The working hypothesis is that [Zn2+] mediates NO-induced apoptosis upon UV-irradiation. The outcomes from this research will not only increase our knowledge of UV-induced and NOS-mediated signaling pathways, but will also lead to a further understanding of regulatory mechanisms and signaling pathways induced by other physiological conditions (e.g., reperfusion, wound healing, diabetes) that are affected by NO and translation inhibition.